Electric Speed Boat

What kind of materials and scantlings will give you 40kg for the hull and deck?

 

Build a plane that floats ! !then power it !!

Anything that is not needed need to go !!also need to find the smallest lightest person !!
Anything from just above the waterline up is waste and not required !! includes topsides and deck and all the bow and not forgetting whats in the stern behind the driver , . Think like Its a plane how would you build it as light as possible ??
Looking at a real case senario that hull should be half its weight or less !! why do you need such a fancy seat ?? why do you need a steering wheel and all the mechnizum that goes with it ,why not a simple Joystick ???

 

Starter batteries are far from ideal for an electric boat, even lithium ones, as what's needed is a good deep discharge capability. Starter batteries are designed to deliver very high current for a few seconds, with very little overall discharge (an engine start only uses a few percent of the battery capacity).

Getting back to the weight budget, and using your assumed figures (noting that the EU average human weight for structural design is generally taken as 86kg, not 75kg).

Hull weight 40kg
Crew weight 75kg
Engine and control weight 100kg
Battery pack weight 80kg

80kg of the very best lithium cells on the market is going to give you a battery capacity of 22.4kWh. Because of the need to maintain the battery pack state of charge within the 30% - 95% range (to give acceptable service life) you have a usable battery pack capacity of just over 14.5kWh.

If you were to draw the equivalent of 140hp, with an assumed motor/controller/wiring losses of 15% (probably optimistic at this power level) then your boat would have an endurance of just over 7 minutes.

I strongly suspect that this much power simply isn't required to give good performance in a boat of this size and weight, it should be able to perform well on less than half that power. What has the power modelling you've done on the hull form revealed? Even a fairly crude estimate using Savitsky's method should give you a ball park figure for required power and is clearly an early part of the design work.

If, say, you were to find that you could get the performance you desire on 70hp, then you double the full speed endurance to 14 minutes. Still not a practical proposition, as the sort of customer for a boat like this will inevitably want to use all the performance all of the time, they are unlikely to accept cruising at 7 or 8 kts, and the hull form will be very unsuited to cruising at this low speed, so will use far more power that it needs to.

At the moment, you can use electric power very effectively for low speed displacement-type boats, provided that care is taken to minimise hull resistance (essentially minimising wetted area and maximising waterline length, for a given displacement). There is a lot of potential for producing an effective inland waterways cruising craft using electric power, as very few designs exist where all the elements (hull, propulsion system, controls etc) are well optimised. As a design project it would be a challenge, as the optimisation process will require a fair bit of work, but the end result may well be just what is needed for some markets (inland waterways day boat hire, for example).

 

http://www.gizmag.com/quadrofoil-electric-hydrofoil-watercraft/22560/pictures#11

Here is one with two seats powered by what looks like a Torqeedo ,that they claim has a range of 62 miles at 24 knots. It went from design to production in six months. They say they are in the process of building a much faster one with a greater range

 

Looks great. Another site with good pics here: http://eluxemagazine.com/eco-tech/wet-wild-an-eco-friendly-jet-ski/ The range/autonomy claims have to be verified, imo. Probably referred to an optimum L/D cruising speed, which is not revealed.

I hope that foils are not in carbon or kevlar and that they're not glue-bonded to the hull, because they will be damaged quite often and will require cheap and fast replacements.

Edit:
I like it a lots!

 

One needs to look carefully at the claims though, and compare them with the specification given!

This electric hydrofoil has a claimed performance of 25mph (22kts), has a 3.7kW motor and a battery pack with a capacity of 4.5kWh. Ignoring the false claim that hydrofoils of this size are more efficient than conventional hulls (they aren't at all, because of the additional power needed to overcome induced drag from the foils), we can nevertheless take a look at whether the claims made for performance stack up.

A 4.5kWh battery pack, if using high specification lithium cells and operated to get a few hundred charge/discharge cycles before the pack needs replacing, will have a usable capacity of approximately 3kWh.

The motor power is stated as being 3.7kW, so the endurance at full power would be about 48 minutes. At 25mph this gives a range of just over 20 miles.

They don't state the minimum foil-borne speed, but it is probably not that much below maximum speed and may well need close to maximum power, so it's unlikely that range would be increased by more than around 50% by going a little more slowly (this is because much of the drag will be induced drag, which is proportional to the lift generated by the foils, rather than the speed through the water).

I note they also claim to have a solar charging option, which stows inside the craft. If we make the bold assumption that they have managed to fold up 2m² of solar panels somewhere in the craft (personally I think they'll struggle to get half this in) then let's take a look at the charging time.

If we optimistically assume they have 2m² of solar panels, pointed directly at bright sunlight, then this would generate about 350W maximum. Average power might be around 100 to 150W through the day. To replenish the 3kWh of used battery power would take around 20 hours of average sunlight, or perhaps 8 or 9 hours on an exceptionally bright day with the panels pointing directly at the sun.

So, in summary the 62 miles quoted range is plainly so optimistic as to be a bit ludicrous, and the solar charging option is, to all intents and purposes, fairly useless from a practical standpoint.

It's an interesting design though, and may well provoke someone to come up with something that's a bit more carefully thought through. One option with this size of battery pack is to make them replaceable, so a discharged unit can be swapped out for a charged one. As a watercraft toy this sort of approach might work, although the cost of the battery packs would be high.

 

Off-topic

While searching for videos about Quadrifoil, i stumbled across this thing: http://youtu.be/bnODhUFGxrc . Not an electric boat, but still a foiler. The base idea is similar to the Quadrifoil, but this one has such an irresistible cyberpunk appearance. And this too was made by Slovenian folks.

 

Claims of speed and range need to be read very carefully. From the gizmag article:

Due to the remarkable efficiency of hydrofoils, it achieves its 25 mph top speed with just one 3.7 kW electric motor, and thanks to its lightweight (150 kg - 330 lb) carbon fiber and Kevlar body and in-built 4.5 kWh lithium batteries, it has a range of 100km (62 miles).​

Two separate claims are made:
1) Top speed of 25 mph
2) Range of 100 km (62 miles)
No claims are made of the range at top speed nor of the speed at the maximum range. This is somewhat common in promotional material for electric boats.

 

Jeremy, you are letting analysis and facts get in the way of the dream.